Key takeaways
- Copper wins on conductivity and spreading, but rarely wins on weight or cost for the whole sink.
- Aluminium extrusions give more surface area per kilogram, which often matters more than raw conductivity.
- A copper base with aluminium fins can capture most of the spreading benefit at a fraction of the weight.
- The finish is part of the material choice: anodising suits aluminium, while copper needs plating or a protective coating.
Conductivity is not the decision
The first number in any heat sink material discussion is thermal conductivity. Copper is roughly twice as conductive as aluminium, so a copper fin conducts heat to its tip more effectively. That sounds decisive, and it often is not. A heat sink has two jobs: move heat from a small source into the base, and pass heat from the surface into the air. The second job is limited by the air, not by the metal.
Air has a low heat transfer coefficient, so the surface area and the airflow set the sink to ambient resistance. Aluminium is light enough to make a large, open sink with a lot of area. Copper is dense, so the same mass gives a smaller sink with less area. In natural convection, the lighter aluminium sink often wins because it can be bigger, even though each fin is less conductive.
The material choice therefore depends on which resistance dominates. If the bottleneck is spreading from a small device into the base, copper helps. If the bottleneck is surface area in still air, aluminium usually helps more per kilogram.
The properties that matter
The table compares 6063 aluminium, the common extrusion alloy, with C11000 copper, the common high conductivity grade. The values are typical handbook figures, not a specification for a particular lot. They are close enough to show the trade-offs and far enough apart to explain why the choice is not obvious.
| Property | Aluminium 6063 | Copper C11000 | Design consequence |
|---|---|---|---|
| Thermal conductivity | About 200 W/m K | About 390 W/m K | Copper conducts along a fin and through a base faster |
| Density | 2.7 g/cm3 | 8.9 g/cm3 | The same volume of copper weighs more than three times as much |
| Specific heat | 0.90 J/g K | 0.385 J/g K | Aluminium stores more heat per gram for a short transient |
| Thermal diffusivity | About 0.83 cm2/s | About 1.13 cm2/s | Copper responds faster to a change in power |
| Coefficient of thermal expansion | About 23 ppm/K | About 17 ppm/K | Copper moves less against a ceramic or a steel package |
| Base metal cost | Index 1 | Index 3 to 4 | Illustrative only. Copper costs more per kilogram and far more per unit volume |
Values are typical handbook figures and are illustrative for comparison. Confirm the temper and the actual conductivity with the material certificate.
Spreading and fin efficiency
Spreading resistance is where copper earns its place. Heat from a small die or a small package enters the base over a limited area, and the base has to carry that heat sideways to the outer fins. Copper's higher conductivity lowers that resistance, especially in a thin base. A copper base can also be thinner than an aluminium one for the same spreading, which saves some of the weight penalty.
Fin efficiency follows the same logic. A copper fin is more efficient at a given height and thickness, so it can be taller or thinner before the tip becomes useless. That matters in a dense forced air sink where height is available but width is not. It matters less in a natural convection sink where the fin height is already limited by the boundary layer.
The gain is not free. A copper fin is heavier, harder to form and more expensive to finish. A copper extrusion is also more difficult than an aluminium one, so many copper sinks are machined, skived or brazed rather than extruded. That changes the tooling and the volume band, not only the material cost.
Weight, volume and vibration
Weight matters in three places: the mounting interface, the shipping cost and the vibration environment. A heavy sink needs a stronger bracket, more fasteners or a support to the chassis. In a vehicle or a handheld product, the added mass can drive a redesign of the housing rather than the sink.
Copper also changes the centre of gravity and the load path. A large copper sink mounted on a thin sheet metal panel can fatigue the panel under vibration, even if the static load is acceptable. The mounting design has to carry the mass, not just the thermal load.
Volume is the other constraint. Copper is denser, so a copper sink of the same shape is heavier but not larger. Where space is fixed and the thermal resistance must come down, copper can be the only option. Where weight is fixed, aluminium gives more surface area and usually more total heat rejection in natural convection.
Cost, supply and finish
Copper costs more per kilogram than aluminium, and the gap per unit volume is wider because copper is denser. The metal cost is only part of the story. Copper is harder to machine, wears tools faster and needs a different finish. Aluminium extrudes into complex fins at low tooling cost, while copper is more often machined or skived, which adds cycle time and scrap.
Finish is a design decision with an electrical consequence. Aluminium can be anodised, which gives corrosion resistance and high emissivity but an insulating surface. Copper does not anodise in the same way, so it is usually left bare, plated with nickel or tin, or coated. A bare copper sink tarnishes, and the oxide layer can affect contact resistance at an earth bond.
Supply also matters. Aluminium extrusion is available in a wide range of standard profiles, so a prototype can use an off-the-shelf sink. Copper grades and thicknesses are less standard, and a custom copper sink may carry a longer lead time. That difference can decide a programme schedule even when the thermal case favours copper.
The hybrid that often wins
A copper base with aluminium fins captures most of the spreading benefit at a fraction of the weight. The copper plate sits under the device and spreads heat into a larger area, then the aluminium extrusion or bonded fin stack carries it to the air. The joint between the two metals is the critical feature, because a poor bond adds a resistance that cancels the gain.
The joint can be brazed, soldered, bonded with a thermal adhesive or clamped with a thermal interface. A brazed or soldered joint has a low resistance and good fatigue life, but it needs a controlled process and a compatible plating. A bonded joint is cheaper but depends on the adhesive thickness and the surface preparation. A clamped joint is serviceable but adds fasteners and pressure.
A hybrid is not automatically better than a well designed aluminium sink. It adds a joint, a supplier and a test. Use it where the spreading resistance is a measured problem, not where it is assumed. A thermal test with a copper spreader and without one will settle the question faster than a material argument.
Selection rules that hold up
Start with the resistance chain. If the sink to ambient term dominates, spend the effort on surface area, fin spacing and airflow, and use aluminium. If the spreading term dominates, consider a copper base or a thicker aluminium base before changing the whole sink to copper.
Check the weight budget and the mounting early. A copper sink that needs a new bracket and a stronger panel is a system cost, not a material cost. Check the finish and the earth bond at the same time, because an anodised aluminium sink and a bare copper sink behave differently at a bonding point.
Finally, ask for the thermal test on the actual assembly. Material data explains the direction of a change, not the size of it. A tested hybrid or a tested aluminium sink with a revised base is worth more than a calculated comparison between two handbook values.
Frequently asked questions
Is a copper heat sink always better than aluminium?
No. Copper conducts better and spreads better, but it is heavier and more expensive, and it usually gives less surface area for the same mass. In natural convection, a larger aluminium sink often outperforms a smaller copper one. The right choice depends on which resistance dominates.
Why use a copper base with aluminium fins?
The copper base spreads heat from a small device into a larger area, and the aluminium fins provide surface area at low weight. The joint between them must be sound, because a poor bond adds resistance and cancels the benefit. A hybrid is justified when spreading is a measured problem.
Can copper heat sinks be anodised?
Copper does not form a useful anodic layer in the way aluminium does. It is usually left bare, plated with nickel or tin, or coated. A bare copper surface tarnishes, and the oxide can affect an earth bond, so the finish and the contact points need to be specified.
Does copper help with thermal cycling?
It can. Copper has a lower coefficient of thermal expansion than aluminium and a higher diffusivity, so it responds faster and moves less against a ceramic package. The benefit depends on the whole stack, including the interface and the baseplate, so it should be tested rather than assumed.
Sources and further reading
- EN 573-3:2019, Aluminium and aluminium alloys. Chemical composition and form of wrought products
- EN 13599:2014, Copper and copper alloys. Copper plate, sheet and strip for electrical purposes
- ASM Handbook, Volume 2, Properties and Selection. Nonferrous Alloys and Special-Purpose Materials
Qumek Engineering Desk
Engineering team
The engineering team behind Qumek drawings, DFM notes, tolerances and inspection standards. Every guide is reviewed against the drawings and processes used on live programmes.
Choosing between an aluminium and a copper sink?
Send the device footprint, the loss and the weight limit. The engineering desk will show where the spreading term sits before the material is fixed.
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